Organic photovoltaics (OPV)[1-7] based on single active layer bulk heterojunction comprising a pair of materials where electron transfer occurs from a donor material to an acceptor material where the pair forms a layer with a higher surface area than a simple flat bilayer structure have been drawing attention because they can be processed from solution at low cost and energy consumption. The most conventional OPV devices consisting of an electron donating polymer such as P3HT and an electron accepting material, such as PCBM, are intensively studied, since they can provide a single active layer bulk heterojunction (BHJ). The morphological structure of blends of polymers is hard to control, but small-molecular OPV system would provide a better control of film morphology. Several concepts have the potential to improve the morphology of OPV devices. One of these is the use of blocking layers to create a so-called p-i-n device. This terminology refers to a structure where the BHJ layer is sandwiched between a pure layer of a dominantly p-type material and a dominantly n-type material. The p and n layers may or may not be electrically doped in this structure. Through the use of convertible materials or orthogonal solvents, these blocking layers can be solution-processed from the same materials in the heterojunction i-layer. Another concept is the ordered heterojunction, in which the donor and acceptor materials form direct paths to the anode and cathode respectively[8] Recently, the use of a spin-cast thermally convertible benzoporphyrin (BP) (FIG. 1 a) has been shown to take advantage of both these concepts.[9,10] This p-i-n device exhibits a power-conversion efficiency of 5.2%, which was successfully demonstrated by spin casting method.[11] However, it is hard to fabricate large areas with spin-casting methods. The alternative processing methods to fabricate larger areas include inkjet printing[12] and slot or blade coating.[13] These methods have worked for polymers such as P3HT[14,15] due to viscous solutions, but small molecule tend to be problematic. More viscous solutions would greatly aid the use of the latter. While adding a polymer additive to the solution to make it more viscous would aid in the use of these methods, the challenge is that the polymer additive cannot diminish the electronic properties of the original materials. A new solution processing method that utilizes a degradable polymer additive would be a great benefit to device fabrication. Similarly, the decomposable polymer additives can be applied to the fabrication of various other organic electronics devices, including but not limited to OFET, OLED, photodetector, sensor and integrated circuit. For example, many polymer, oligomer, dendrimer and small molecule semiconductors had been developed for OFET and OLED devices by printing or coating process.[16-24] Again, certain solution viscosity is generally required for the printing or coating process which could be difficult to achieve from the semiconductor solution especially when the semiconductor or semiconductors are small molecules, oliogmers or dendrimers. A decomposable polymer additive which increase the solution viscosity at the coating step and which then is removed later by annealing could dramatically improve the film quality so as the device performance.
Poly(propylene carbonate) (PC) (FIG. 1b) derived from carbon dioxide and propylene oxide has attracted practical interest with respect to the CO2 fixation and biodegradability.[25] PC also exhibits high transparency and superior mechanical strength. The carbonate linkage in the backbone of PC results in a relatively low thermal decomposition temperature (Td), potentially limiting its practical applications. But from another point of view, the lower Td and decomposing properties could be beneficial for certain applications. Novomer, Inc. has claimed that its synthetic procedure is able to produce PC which decomposes more uniformly at lower temperatures with extremely low residue left after the annealing process. TGA analysis shows that PC can degrade 100% completely above 200° C.